Clinical color Doppler ultrasound technology is a popular, non-invasive, real-time, relatively inexpensive imaging modality, which currently allows the 2D visualization of blood flow within the heart and the vascular system. Doppler ultrasound flow velocity measurement is important for the determination of blood/oxygen supply to various organs, arterial wall shear stress, and blood-tissue gas exchange, as well as for the evaluation of myocardial and valvular function. Initially, we have chosen to concentrate on the structure and flow in the carotid artery, due to the simplifications which this geometry allows. We have assembled instrumentation within a clinical echcardiography laboratory, to acquire color Doppler ultrasound images along with time-encoded position/orientation data for the handheld transducer. A carotid artery/neck phantom was designed and fabricated, to allow for calibration and testing of both the position/orientation measurement subsystem and the Doppler flow velocity measurement subsystem. Flow velocity images have been transferred from the HP SONOS 1500 ultrasound system, as separate digital values of structure and flow velocity, onto the Macintosh Quadra 950 microcomputer which is the heart of our image reconstruction system. All algorithms and procedures for correcting the flow velocity readings have been designed and outlined in detail, and all software has been described in flowcharts. A patent application, covering the basic algorithm for correcting the color flow velocity measurements, is in process. This project is otherwise, currently inactive at the NIH, however, work in this area is continuing at the Technion in Israel, under the direction of the PI. It is hoped that our contribution may eventually find wide use in the non-invasive measurement of blood flow velocity, in research as well as in clinical practice.